The present invention relates to an X-ray exposure apparatus, and particularly, to one capable of effectively adjusting an alignment of an axis of radiated X-ray beams of the X-ray exposure apparatus with an optical axis of an optical alignment system of the X-ray exposure apparatus and a method of positioning the X-ray exposure apparatus.
In a known technology, a light exposure device has been generally utilized for forming a large scale integrated circuit (LSI) pattern, but recently, the formation of patterns by light exposure device has approached its limit in resolution for the requirement of the formation of extremely fine LSI patterns.
In view of this limit, recently, an X-ray exposure apparatus capable of forming a fine LSI pattern in comparison with the light exposure device are being searched and developed. The X-ray exposure device requires an X-ray source provided with high luminance and, in this viewpoint, an attention has been paid to synchrotrons as X-ray sources.
A conventional X-ray exposure apparatus provided with a synchrotron as the X-ray source will be described hereunder.
X-ray beams generated from the synchrotron are reflected by a reflecting mirror and then enter a chamber of an exposure apparatus body of the exposure apparatus. The interior of the chamber is of a helium atmosphere for preventing the X-ray beams from being attenuated, and in the inside of the chamber are accommodated a mask stage holding an X-ray mask that is movable, a wafer stage holding a semiconductor wafer to be movable and an alignment optical system for detecting a positional offset between patterns described on the X-ray mask and the semiconductor wafer.
According to this structure of the X-ray exposure apparatus, X-ray beams entering the chamber of the X-ray exposure apparatus body are irradiated on the X-ray mask, and then irradiated on the surface of the semiconductor wafer to thereby expose a circuit pattern of the X-ray mask onto the semiconductor wafer.
The exposure apparatus body is mounted on an oscillation removing table which is set on a floor through an elastic member such as air spring, thus effectively preventing the exposure apparatus body from being oscillated or affected by an external shock or the like from the floor.
The X-ray beams obtained by a synchrotron orbit radiation (SOR) constitute horizontal linear beams irradiated in a horizontal direction. In order to enlarge an irradiated area for carrying out an exposure transfer of the circuit pattern of the X-ray mask onto the semiconductor wafer, an X-ray reflecting mirror is arranged between the synchrotron and the exposure apparatus body, and the X-ray beams are swinged by swinging the reflecting mirror.
Furthermore, in order to transfer the circuit pattern on the X-ray mask onto the semiconductor wafer in a precisely overlapped manner, it is required that the alignment optical system and an exposure optical system for the transfer be stably constructed with a predetermined performance. This requirement, in one example, is achieved by assembling, for adjustment with mechanically high precision, the mask stage, the wafer stage and the alignment optical system as the exposure apparatus body.
For the reason described above, in the X-ray exposure apparatus utilizing the SOR, the adjustment of the axes of the X-ray beams and the alignment optical system are required to have high precision.
In other words, in order to carry out transferring, in a precisely overlapped state, the circuit pattern on the X-ray mask to the semiconductor wafer on which a resist is coated, it is necessary to adjust the positions of the X-ray mask and the semiconductor wafer so as not to have a positional offset between a position of a mask pattern and a position of a pattern to be formed on the semiconductor wafer. Namely, the precise coincidence of the optical axis of the X-ray beams with an optical axis, as measurement reference, of the alignment optical system is required. In the case of no coincidence, a positional offset is caused in an amount such as shown by the following equation, EQU .delta.=G.times..DELTA..theta.
in which G is a gap between the X-ray mask and the semiconductor wafer, and .DELTA..theta. is an angular difference between the axis of the beam and the axis of the alignment optical system, and .delta. is an amount of positional offset.
As described above, the X-ray beams are reflected by the reflecting mirror and then enter the exposure apparatus body, so that the X-ray beams are not ordinarily parallel to the floor on which the X-ray exposure apparatus is settled and has an inclination of several angles. On the contrary, since the exposure apparatus body is precisely assembled with a horizontal plane as the reference level, the optical axis of the alignment optical system as the measurement reference is made substantially horizontal.
For this reason, in the prior art, in order to make the axis of the X-ray beams coincident with the optical axis of the alignment optical system as the measurement reference, there is provided a method wherein two parallel X-ray reflecting mirrors are arranged with a predetermined distance therebetween between the synchrotron and the exposure apparatus body to thereby reflect the X-ray beams twice by the two reflecting mirrors to obtain horizontal light beams. In another method, an angle of the X-ray reflecting mirror is generally adjusted in accordance with the arranged position and the inclination of the exposure apparatus body.
In the former prior art method, however, since the X-ray beams are twice reflected by the two X-ray reflecting mirrors, the X-ray beams are largely attenuated. However, in the latter prior art method, since the inclination of the X-ray reflecting mirror is offset with respect to the optimum inclination according to the location or inclination of the exposure apparatus body, the X-ray beams cannot be effectively utilized, and hence the function of the X-ray exposure apparatus utilizing the SOR cannot be adequately attained.